We plan to demonstrate chromosome changes resulting from treatment of rat diploid cells in culture with chemical carcinogens using polycyclic aromatic hydrocarbons and alkylating agents. We expect to correlate these changes with evidence for transformation in vitro and oncogenesis in appropriate host animals. Using new methods (fluorescent banding and special Giemsa stains) which demonstrate intrachromosomal structure, we expect to localize some of the early interactions of carcinogens with the genetic material. A series of chemical blocking and substitution experiments with special stains may help to define the basic structural organization of chromosomes as well as to illustrate the interaction between the chemical carcinogens and the chromosomes.